The invention relates to a method of making a current sensor having a magnetoresistive element configured into a bridge. The sensor may be used to measure DC, AC, or pulsed current and, particularly, high currents of the order of a few amps to several hundred amps.
It is known to employ thin film permalloy (Ni/Fe) magnetoresistive bridge sensors (hereforth called MR sensors) as power converters in the design of electrical energy meters (see, for example, the IEEE Transactions on Magnetics, VOL. MAG-20, No. 5, September 1984, pages 966-968-Kwiatkowski et al). It is also known to employ Barber-pole biasing with MR sensors, for sensing magnetic fields, in order to provide a linear bridge output (see, for example, the IEEE Transactions on Magnetics, VOL. MAG-18, No. 6, November 1982, pages 1149-1151-Tsang and Fontana). However, to the best of our knowledge, no successful attempt has yet been made to mass-produce devices employing MR sensors which are primarily intended for sensing current.
The present invention provides a method of making a current sensing device by mounting an MR sensor on a conductive member. Such a sensor responds to the magnetic field created by the current flowing in the conductive member, the output of the bridge being proportional to the current flow. Whilst it may appear to be a relatively straightforward matter to manufacture such a device, a technique must be found for mass-producing devices having consistent performance characteristics. For example, the resistance of the sensor depends on the strength of the magnetic field in the region where the sensor is located and variations in the spacing between the sensor and the conductive member can have a drastic effect on field strength. This leads to the problem of trying to position the sensor accurately with respect to the conductive member. The present invention seeks to solve this problem.